The present exemplary embodiment relates to thermal systems. It finds particular application in conjunction with a thermal control of the printer fuser and will be described with a particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other thermal control systems and like applications.
In a typical xerographic marking engine, such as a copier or printer, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to a print medium, such as a sheet of paper. The fusing of the toner onto the paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure to fuse and permanently affix the powder image to the copy sheet.
In order to fuse and fix the powder toner particles onto a copy sheet or support member permanently as above, it is necessary for the thermal fusing apparatus to elevate the temperature of the toner images to a point at which constituents of the toner particles coalesce and become tacky.
Typically, when started up, each reproduction machine goes through a warm up phase during which the heated member of the fusing apparatus gradually warms up to where the fusing channel or fusing nip reaches and can be maintained at the high fusing temperature. After that, the machine can be activated to run a job reproducing images through a run or operating cycle. After one of such jobs, the machine may be idle or go into an idle or a standby mode, while waiting for the next reproduction job.
The fuser roll is a large thermal mass whose temperature must be controlled to tight tolerances for a good quality print job. When the print media enters the system, the fuser roll surface temperature begins to drop. Typically, the current PID temperature controller runs a standard temperature control algorithm which lacks speed and gain to bring the fuser roll surface temperature back to steady state in a short period of time. As a result, during the beginning of a large print job, the fuser roll surface temperature substantially drops. Once the temperature of a fusing apparatus starts to drop or fall, the fuser roll acquires a thermal inertia which makes reversal or recovery difficult. As the standard temperature control algorithm brings temperature back up to the fusing temperature, it causes an overshoot by the end of the job. The problem might cause some print imperfection.